Transistors are used as switches in many integrated circuit systems. By altering the voltage at the gate of a transistor, current flow between the source and drain may be controlled. Transistor-based switches may be used in both single-ended signal systems, and in differential signal systems.
One problem with transistor-based switches is that when the voltage on the terminals of the switch exceeds supply or goes below ground, the switch may turn on when it is supposed to be off. Previous methods of solving this problem have generally utilized multiple sets of transistors so that at least one transistor between the terminals of the switch would remain off regardless of voltage swings. However, these implementations will tend to increase the area costs consumed by the switch, as well as increasing load capacitance and leakage on the terminals. In some implementations, such as when used as part of a differential termination scheme, the transistors in the switch may have to be sized to achieve a predetermined overall resistance between the terminals of the switch. The requirement for the switch to achieve a certain resistance may potentially further increase the area costs of switches with multiple sets of transistors.
Thus, there may be a need for an area-efficient switch that remains off even when the voltages at the terminals of the switch exceed supply or fall below ground.